Permalink : cart

Hello,
I have just installed woocommerce. When i want choice permakink as …/%postname%/ i get 404 on cart page, no on the others pages.
If i leave …/?p=123/ it is ok. But no recommanded for SEO. (i precise i use wp since about 10 years).
my htacess is

SetEnv PHP_VER 5_4

#langue caractere
AddDefaultCharset UTF-8

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ – [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

# END WordPress

how resolve that ? where i do mistake ?
precision before i used wp e-commerce, it has some differents inconveniants (!), i am doing a new site e-commerce.
http://www.artisanathai.fr/

http://wordpress.org/extend/plugins/woocommerce/